The C-proteins complex with heterogeneous nuclear RNA (hnRNA) to form a unique 19S complex. In their absence, the A- and B-group proteins form structures not found in native heterogeneous nuclear ribonucleoprotein (hnRNP). The C-protein complexes appear to be dodecamers composed of three C-protein tetramers (C1)3C2. Originally, it was thought that three tetramers bound to RNA, but it appears that three tetramers can self-assemble as well. Mass measurements of these structures should show if they are indeed tetramers. Unfortunately, these specimens seemed to have a large amount of denatured protein in the STEM. Further work is needed to eliminate this.